1. Field of the Invention
This invention relates to a high load gas combustion apparatus for use mainly in domestic combustors, in which a fan is used to forcibly supply air for burning to promote combustion reaction and shorten the flame length, thus achieving reduction in size of the combustion chamber and hence the entire apparatus, and in which the fan is a relatively small-sized fan to provide low supply pressure for ensuring combustion at a low noise level.
2. Prior Art
In a conventional high load gas combustion apparatus in which air for burning is supplied forcibly, air ports of different sizes were arranged in the form of multiple stages relative to the direction of flow of a mixture, and secondary air was supplied to the flame at a fairly high speed mainly for the purpose of effecting turbulent combustion. A typical example of such an apparatus is disclosed in U.S. Pat. No. 3,494,711, which is shown in FIG. 1. The illustrated example is a burner for installation in a flow of high-speed gas of low oxygen concentration. A mixture flows into a combustion chamber 4 from a mixture chamber 2 formed in a burner body 1 through flame ports 3 comprising a number of small holes arranged in the form of a longitudinal row. Fresh air passes both sides of the burner body 1 from a supply chamber 5 and then reaches a fresh air chamber 6. Some fresh air is supplied to the combustion chamber 4 through parallel air ports 7 which comprise a number of relatively small holes and are arranged near the flame ports 3, while the remaining fresh air is supplied to the combustion chamber 4 through oblique air ports 9 which comprise a number of relatively large holes and are arranged in an oblique plate 8.
The burner thus constructed has the following disadvantages:
(1) The flow rate of fresh air jetting out of the parallel air ports 7 becomes nearly equal to that of fresh air jetted out of the oblique air ports 9 because of the absence of a special means for reducing pressure. For this reason, when air supply pressure produced by the fan is raised, the flow rate of fresh air from the parallel air ports 7 is increased correspondingly so that the effect of flame retention will be lost;
(2) Because the oblique air ports 9 and jet ports 12 are bored in the form of multiple stages in the oblique plate defining the combustion chamber to supply fresh air and gas of low oxygen concentration, respectively, flames formed to extend toward the downstream side are disturbed by air jetted and supplied from the oblique air ports 9 or jet ports 12 located on the relatively upstream side. Particularly, in the case of using gas fuel having lower combustion velocity, there are produced discontinuous and unsteady flame zones, thus resulting in high combustion noise; and
(3) The flame ports 3 comprise a number of small holes arranged in the form of a longitudinal row and the total area of flame ports is small. With the increasing combustion rate, therefore, the mixture supplied from the flame ports has a higher jet speed, whereby the aforesaid disturbance of unsteady flame zones is enlarged and the combustion noise is correspondingly further increased.
These disadvantages made it impossible for the prior art apparatus to be directly applied to domestic combustors which require a low noise level and compactness, and to be universally used for various types of gas fuel.